Flow-through steam generator

ABSTRACT

Flow-through steam generator includes a boiler system having a heating zone and a nonheating zone, means for measuring boiler pressure loss and throughput at locations in the nonheating zone of the system, and load correction regulator means operatively connected to the measuring means and responsive to the measured data for adjusting feedwater supply and heat power input to the boiler system so that the feedwater supply and the heat power input are proportional to one another.

tee ate Inventor Appl. No.

Filed Patented Assignee Priority Michel Rupprecht Erlangen, Germany Dec. W, 1963 Fell. 9, 1971 Siemens Alrtiengesellschaft Beriin, Germany Dec. 12, 1967, Dec. 15, 1967 Germany P 15 76 882.8 and P 15 76 883.9

FLOW-UUGH STEAM GENERATOR 10 Claims, 5 Drawing lFigs.

US. Cl 122/32, 122/448 lint. Cl F221) 1/02 Field of Search 122/32,

[56] References Cited UNITED STATES PATENTS 1,975,086 10/1934 Dickey 122/448 3,154,473 10/1964 Martin 176/60 FOREIGN PATENTS 384,832 12/1932 Great Britain 122/451 Primary Examiner-Kenneth W. Sprague Atzorneys-Curt M. Avery, Arthur E. Wilfond, Herbert L.

Lerner and Daniel J. Tick ABSTRACT: Flow-through steam generator includes a boiler system having a heating zone and a nonheating zone, means for measuring boiler pressure loss and throughput at locations in the nonheating zone of the system, and load correction regulator means operatively connected to the measuring means and responsive to the measured data for adjusting feedwater supply and heat power input to the boiler system so that the feedwater supply and the heat power input are proportional to one another.

FLOW-THROUGH STEAM GENERATOR My invention relates to flow-through steam generator and, more particularly, to such generators wherein the entire tube system does not have any intermediate connection of collection vessels or manifolds or other mixing and separating vessels, and is heated by a heat carrier which does not soil the heating surfaces or coils of the tube system. The invention is of particular significance for flow-through steam generators that are heated by the thermal output of nuclear reactors wherein, for example, a coolant gas of the reactor is employed as the heat carrier.

In the case of a Co -cooled reactor having a gas temperature of 650 C, for example, no ferritic materials can be employed any more in constructing the last portion of the superheater of the system, even if the steam temperature is kept suitably lower. One is then forced to construct the superheater of austenitic steels because the carbon dioxide gas would otherwise attack or corrode the ferritic materials at the high temperatures.

As is well known, however, austenitic materials are very sensitive to temperature shock. Such temperature shock must be anticipated when there is rapid transition from one operating condition to another or when the heat input to the system suddenly drops. In order to avoid such temperature shocks in conventional flow-through steam generators that are heated with fossil fuels, one could heretofore apply therein measures for preventing oversupply to the boiler or other temperature jumps that are dangerous to the superheater of the system. In conventional boilers, temperature measurements are generally made at suitable locations between the heating surfaces or coils; in addition thereto, or even independently thereof relatively cold steam or even liquid working medium has been effectively prevented from reaching the superheater by the installation of bottles, separating vessels or other devices in the tube system.

In contrast to the foregoing constructions of conventional boilers, in a flow-through or once-through steam generator of the aforedescribed type, it is not advisable or even possible to provide temperature measuring locations, separating vessels or the like within the boiler zone that is being heated, due to the fact that the flow-through steam generator is formed of many tube strings extending parallel to one another and are traversed by feedwater in counterflow to CQ gas without mixing locations, so that there is no possibility of installing thereat any bottle offering resistance or any mixing location for providing troublefree temperature measurement. One might perhaps consider affixing thermocouple elements or other temperature measuring devices to a selection of the numerous parallel strings of the flow-through system; however, such a measure would not be adequately fail-safe for a reactor boiler since these measuring locations are no longer accessible after assembly of the reactor. Furthermore, the measuring apparatus must be capable of withstanding occasionally great mechanical stresses exerted by the CQ g'as flowing at relatively high velocity.

It is accordingly an object of my invention to provide flowthrough steam generator-which avoids the foregoing disadvantages.

My invention is based on the idea that instead of taking temperature measurements within the heated zone of the boiler, the pressure loss of the boiler at full load or other defined load conditions and at full live stem temperature can be employed as measure for the correct ratio of feedwater to heat input. Thus, for constant feedwater supply and decreasing heat input, the pressure loss decreases considerably in accordance with the characteristics of the flow-through boiler. For every specific boiler, quite specific relationships exist between feedwater supply and heat power supply for each load. One is therefore in a position by means of continuous monitoring of the feedwater supply and of the pressure loss at predetermined final temperature, to draw proper conclusions and to recognize timely or punctually the danger of excessive feedwater supply to the boiler when the heating is defective, before the excessive water supply has an effect on the final temperature.

With conventionally heated boilers, no trouble-free results could be achieved by this method, because one always had to consider soiling of the heating surfaces in conventional boilers and, moreover, due to the larger component of radiation heat, in contrast to the smaller component of convection heat, no clearly defined relationships prevail. Only if, as is the case for a Co -cooled reactor, a clean heat carrier washes around or contacts the heat surfaces and does not deposit any sediment thereon, can such a method operate with adequate safety.

With the foregoing and other objects in view, I provide in accordance with my invention, flow-through steam generator comprising a boiler system having a heating zone and a nonheating zone, means for measuring boiler pressure loss and throughput at locations in the nonheating zone of the system, and load correction regulator means operatively connected to the measuring means and responsive to the measured data for adjusting feedwater supply and heat power input to the boiler system so that the feedwater supply and the heat power input are proportional to one another, whereby temperature shock in a superheater of the boiler system is avoided at transition from one operating condition of the boiler system to another.

In accordance with a further feature of my invention, a device is connected to the load correction regulator means upstream thereof wherein the measured data are compared with stored, previously calculated and determined specific relationships between feedwater supply, pressure drop and end temperature, and are evaluated.

An impairment of the measuring results can only be caused in substance by the fact that the inner walls of the boiler system tubes are subjected to roughening, deposition of sediments and other known changes which affect the flow-through resistance of the tubes. These changes occur so slowly, however, that it is sufiicient only to test the pressure loss periodically and to effect a correction of the predetermined nominal value. This can be carried out manually or continually by automatic means.

In accordance with my invention, 1 provide means for bringing the feedwater supply and heat power input into accord or proportion with one another for all sudden changes in load, the load correction regulating means being adapted to transmit a signal for regulating the feedwater supply, the heat supply or both.

In accordance with other features of my invention, I provide measuring devices having different measuring ranges for determining the pressure loss of the flow-through system for different load ranges so as to afford thereby a sufficiently accurate result both for high heat input as well as for low heat supply. Thus, by employing several of such pressure loss measuring devices at various load levels, an automatic switch-over from one measuring device to another can be effected.

Other features which are considered as characteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as embodied in flow-through steam generator, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing, in which:

FIG. 1 is a schematic view of a flow-through steam generator constructed inaccordance with my invention;

FIG. 2 is a cross-sectional view through the steam generator groups and reactor of FIG. 1;

FIGS. 3 and 4 are plot diagrams of pressure loss against feedwater supply-and showing their relationship for several different final temperatures of the generated steam; and

FIG. 5 is a schematic view corresponding to that of FIG. 1 of another embodiment of the flow-through stem generator of my invention.

Referring now to the drawing drawings and first particularly to FIGS. 1 and 2 thereof, there isshown an embodiment of the flow-through steam generator wherein CO gas, heated for example to 650 C, is conducted from a reactor core in direction of the arrow 2 to steam generator groups 3 to 10. As shown diagrammatically, circulating blowers 11 are provided respectively for the individual steam generator groups. Feedwater is supplied to the steam generator groups 3 to from below through inlet manifolds l2 located outside the reactor walls l. The steam generator tube system continuously and exclusively rises from the manifolds 12 without any intermediate connection with any collecting vessels or other manifolds, mixing vessels, water-steam separating vessels or the like and terminates in outlet manifolds 13 to which steam outlet conduits M are connected. Since all of the heating surfaces or tubes are mounted within the reactor walls 1 and, after having been installed therein, are no longer accessible from the exterior, it does not appear to be advisable to mount any temperature measuring devices in this region.

While avoiding temperature measuring locations in the region of the heating surfaces, I provide, in accordance with my invention, other means and measures for preventing oversupply of feedwater to the flow-through boiler and thereby protect the austenitic final superheater against temperature shock. My invention is based on the phenomenon that, for a decreasing steam temperature while the supply of feed water to the boiler is constantly maintained, the flow-through resistance of the flow-through system diminishes considerably if the balance between reactor heat supply and feedwater supply is no longer afi'orded, so that from the reduction in the pressure loss to be observed one can assume a reduction in the heating, which then results in a reduction in the final temperature of the steam.

The foregoing relationship is illustrated in FIG. 3, which is a diagram of the pressure loss Ap of a flow-through steam generator plotted against percentage of feedwater supply Q. For a full I00 percent supply of feedwater and the aforementioned final temperature of 530 C. for a live steam pressure of I70 atmospheres absolute (ata) represented by the curve a, the pressure loss in the illustrated embodiment of FIGS. 1 and 2 is about 7.5 at. The flow-through steam generator of my invention is thus operated with a feedwater supply suitably reduced in accordance with the amount of instantaneously demanded or available power of the installation, the live steam temperature being always maintained constant at the full value thereof. Due to the fact that the square of the pressure decrease in the boiler is proportional to the throughput of the feedwater, there is no linear relationship between the feedwater supply and pressure loss, disregarding the fact that the volume increases of the working medium dependent on the heating and vaporizing as well as on the superheating also have an effect on the relationship therebetween. An exact adjustment of the flow cross section of the tube system to the volume increase would be practically impossible because, due to branching or transition to larger tube cross sections, the increased volume is only taken into account stepwise, and moreover with a Benson-type or once-through boiler, the vaporizing zone wanders in dependence on the load. Therefore, for every boiler, the course or path of the pressure drop must be individually determined.

Since the volume increase of the working medium along the entire path thereof through the tube system is greatly temperature-dependent, the pressure loss in the boiler is therefore also greatly dependent on the heating level of the working medium, which results in the aforementioned level of the outlet temperature of the steam. The significance of the foregoing is therefore that for the same quantity of supplied feedwater, the pressure loss is lower if the heating of the working medium diminishes and the aforedescribed final temperature at the steam outlet is no longer attained.

FIG. 3 shows the pressure loss curves a, b and c in dependence on the feedwater supply, wherein the curve a, as aforementioned, depicts the heating of feedwater up to a final temperature of 530 C. at maximum feedwater supply, whereas curves b and c, respectively relate to heating up to final temperatures of 480 C. and 430 C. at maximum feedwater supply. If the boiler is operated, for example at the point P, i.e. at percent feedwater supply and the aforementioned final temperature of 530 C., and heat supplied is suddenly reduced so that the final outlet temperature would be 430 C., the operation of the boiler would then be at point Pl on the curve 0. The boiler would then be oversupplied with feedwater so that the danger would then arise of the end or final superheater being subjected to a temperature shock. In order to prevent this from occurring, the regulation must take effect punctually.

If one wished to regulate the steam outlet temperature only, such regulation could not equalize or compensate for sudden load changes, because the regulation would be applied too late, namely only after an undue temperature reduction in the vicinity of the final superheater had already occurred. With the data regarding the boiler characteristics according to the curves a, b and c of FIG. 3, it is readily apparent, however, that one must take into consideration the quite specific relationships to one another of outlet temperature, pressure loss and feedwater supply in order to maintain the aforedescribed 0utlet temperature. As shown in FIG. 3, the drop from point P to point Pl represents a reduction in pressure loss of 1.87 at. This diminished value of the pressure loss corresponds to the pressure loss value at the boiler operating point P2 on the curve a. If the feed water supply should now be reduced from 90 percent to 75 percent, then the boiler operating point would again lie on the curve a and the outlet temperature of the steam would thereby be maintained at its aforedescribed level, i.e. 530 C. The readily austenitic end or final superheater would thereby be protected from a harmful temperature jump.

The characteristic data corresponding to that supplied by the curves a, b and c of FIG. 3 should be determined beforehand, for every boiler. The device 25 shown in FIG. 1 serves for storing predetermined nominal values which take their relationships into consideration. To effect the regulation, as shown in FIG. 1, the pressure difference Ap is obtained for example with a differential pressure measuring instrument 26 or by means of separate pressure measuring devices located at the boiler inlet and outlet. A signal representing the measured value characteristic of the pressure drop is then transmitted over the signal line 27 to a comparator device 28 in which a comparison and an evaluation of the signal transmitted thereto is made. Furthermore, the respective quantity of feedwater is measured by measuring diaphragm or orifice 29 or any other suitable flow-through measuring device and the measured value is passed over the signal line 30 to a comparing and evaluating device 28, while on the other hand, the stored nominal value is transmitted thereto from the storage device 25 through the signal line 31. A load correction regulator 33 is then acted upon by the comparing and evaluating device 28 over the operating line 32 in accordance with the signals delivered to the device 28. The load correction regulator 33 is connected on the one hand, through the operating line 34 with a feedwater regulator 17 which is operatively connected to a feedwater pump 18 and/or a feedwater regulating valve, and on the other hand, may be connected, as represented by the operating line 35, to suitable equipment 50 for regulating the nuclear reactor proper. The operating lines referred to hereinabove are merely representative of any suitable electrical, mechanical hydraulic or similar means known to the man of ordinary skill in the art of exerting an influence on one device by another.

Thus, if in the aforedescribed case, the outlet temperature threatens to drop due to oversupplying the boiler with feedwater, the pressure-difference measuring device 26 registers a reduced pressure loss in the boiler, so that for an initially constant feedwater supply measured by the orifice plate 29, the comparing and evaluating device 28, upon comparison of the measured constant feedwater supply and the reduced pressure loss with the nominal values provided in the storage device 25,

transmits a signal to the load correction regulator 33 which orders a reduction in the supply of feedwater by suitably actuating the pump 18 and/or the valve 19 through the feedwater regulator E7 or orders an increase in the heating power supplied to the boiler by suitably actuating the reactor regulating devices 50 to effect a higher thermal output from the reactor.

In order to take into account the occurrence of pressure loss increases, for example due to soiling or roughening of the inner surface of the boiler tube system, in the course of time, a nominal value correcting device 36 can be provided by which the nominal value stored in the device 25 can be manually adjusted. It is also possible, however, as indicated by the signal line 37 to effect automatic adjustment of the nominal value correction by continuous monitoring thereof with any suitable conventional monitoring device. Moreover, the final temperature of the working medium at the steam outlet 14 is continuously monitored at the measuring location T, and the measured value transmitted through the signal line 40 to the comparing and evaluating device 28.

For the region of the steam generator portion or group 7, a connecting conduit 13' is provided between the inlet distributor l2 and the outlet manifold 13. A device 24 corresponding to a type of Barton cell is connected in the conduit 13' for providing an indication of a partial filling of the tube system with feedwater when the boiler is inoperative or is being operated at partial load. According to an earlier proposal of mine in my copending application Ser. No. 78 1,931, filed Dec. 6, 1968, (R3961) for facilitating startup and restart of such a boiler, I have proposed that the tube system be only partially, for example half-filled with water and then, to monitor the water level from the outside. A device in the form of a Barton cell is suitable for providing such an indication of the extent to which the boiler is filled with feedwater. In the embodiment of my invention in the instant application as shown in FIG. 1 thereof, a second Barton cell 33 is also provided which is capable of sustaining the entire full load differential pressure of 7.5 ats. In the event the accuracy of the Barton cell 38 should no longer be sufficient for delivering a satisfactory measuring signal when the load falls below the half-load value, an additional Barton cell 39 is provided, which operates within an intermediate measuring range. In a manner similar to that for the differential pressure measuring device 26, a signal is transmitted from the Barton cells 24,38,39 39 to the comparing and evaluating device 28. It is thereby possible to effect a load-dependent automatic switch-over from one to the other device for the different load levels.

In accordance with a further feature of my invention, for sliding pressure operation, i.e. at load-dependent variable operating pressure, a nominal value correction is effected. Thus, for sliding pressure operation, under continuous transmission of measurement signals representing the load and the steam pressure, the respective pressure loss of the boiler is calculated in a device connected forward of the load correction regulator so that a nominal value adjustment can then be effected in the vicinity of the nominal value storage device.

In the diagram of FIG. 4, the pressure loss Ap of a flowthrough steam generator is shown plotted against the feedwater supply 0, in a manner similar to that shown in FIG. 3.

Whereas the curves a, b and c apply to a fixed or steady pressure operation of, for example, 170 atmospheres absolute pressure (ata), the curves d, e and f represent pressure losses at sliding pressure for the corresponding outlet temperatures of 530, 480 and 430 C. Pure sliding pressure operation means that the live steam pressure decreases in proportion to the load. As shown by the lines g, h and i, pressure loss values of Si, 86 and 119 ata are indicated respectively at feedwater supply values of 30, 50 and 70 percent.

In order to ensure the utilization of the aforedescribed principle also for sliding pressure, a calculator can be used which determines the nominal value of the flow-through pressure loss dependent upon the loadand the operating pressure and compares it to the actual value. For a pressure loss deviating from the nominal value in comparison to the load, the quantity of feedwater must be increased or reduced until the actual value and the nominal value are equal.

In the embodiment shown in FIG. 5, there is shown a device 41 to which measurement values corresponding to the steam pressure at P are transmitted over the signal line 42. Moreover, measurement values dependent upon or d corresponding to the load at L are conducted over the signal line 43 to the device 41. The device 41 can then either have an operative effect directly on the nominal value storage device 25 through the signal line 44 in the manner shown in FIG. 5 or can effect at another location 36 in a manner previously described with regard to FIG. 1 a correction of the nominal value supplied by the storage device 25. Like reference numerals in FIGS. 1 and 5 represent similar members.

Iclaim:

l. Flow-through steam generator comprising a boiler system having a heating zone and a nonheating zone, means continuously measuring boiler pressure loss and throughput at locations in the nonheating zone of said system, load correction regulator means operatively connected to said measuring means and responsive to the measured data for adjusting feedwater supply and heat power input to said boiler system so that said feedwater supply and said heat power input are proportional to one another, and means for continuously measuring the final temperature in said nonheating zone of steam generated in said system, said last-mentioned means being operatively connected to said load correction regulator means.

2. Flow-through steam generator according to claim I wherein said boiler system comprises a tube system located in said heating zone and devoid of any intermediate connection with any vessels, said tube system having heating surfaces engageable by a nonsoiling heat carrier.

3. Flow-through steam generator according to claim 1, comprising a nuclear reactor primary circulatory system for circulating a coolant gas heated by said reactor, said heat carrier being said heated coolant gas.

4. Flow-through steam generator according to claim I comprising a device connected downstream of said load correction regulating means for comparing the measured data with predetermined relationships between feedwater supply, pressure drop and final temperature, and evaluating the same.

5. Flow-through steam generator according to claim 1, including means for providing nominal values corresponding to the measured data, and means for correcting said nominal values in adjustment with varying pressure loss values.

6. Flow-through steam generator according to claim 5 wherein said nominal values correcting means are manually operable.

7. Flow-through steam generator according to claim 5 wherein said nominal values correcting means are automatically operable.

8. Flow-through steam generator according to claim 1, including measuring devices of different measuring ranges for determining pressure loss in said boiler system for different load ranges.

9. Flow-through steam generator according to claim 8, including automatic switch-over means between said pressure loss measuring devices for effecting load-dependent switching from one to another of said measuring devices at different load levels.

10. Flow-through steam generator according to claim 1, including storage means for providing nominal values for comparison with the measured data, a calculating device operatively connected to said load correction regulator means downstream thereof for calculating the respective pressure loss of said boiler system for load-dependent variable operating pressure, means for continuously transmitting measurement signals representing load and steam pressure to said calculating device, and means located in the vicinity of said nominal values storage means for adjusting said nominal value. 

1. Flow-through steam generator comprising a boiler system having a heating zone and a nonheating zone, means continuously measuring boiler pressure loss and throughput at locations in the nonheating zone of said system, load correction regulator means operatively connected to said measUring means and responsive to the measured data for adjusting feedwater supply and heat power input to said boiler system so that said feedwater supply and said heat power input are proportional to one another, and means for continuously measuring the final temperature in said nonheating zone of steam generated in said system, said lastmentioned means being operatively connected to said load correction regulator means.
 2. Flow-through steam generator according to claim 1 wherein said boiler system comprises a tube system located in said heating zone and devoid of any intermediate connection with any vessels, said tube system having heating surfaces engageable by a nonsoiling heat carrier.
 3. Flow-through steam generator according to claim 1, comprising a nuclear reactor primary circulatory system for circulating a coolant gas heated by said reactor, said heat carrier being said heated coolant gas.
 4. Flow-through steam generator according to claim 1 comprising a device connected downstream of said load correction regulating means for comparing the measured data with predetermined relationships between feedwater supply, pressure drop and final temperature, and evaluating the same.
 5. Flow-through steam generator according to claim 1, including means for providing nominal values corresponding to the measured data, and means for correcting said nominal values in adjustment with varying pressure loss values.
 6. Flow-through steam generator according to claim 5 wherein said nominal values correcting means are manually operable.
 7. Flow-through steam generator according to claim 5 wherein said nominal values correcting means are automatically operable.
 8. Flow-through steam generator according to claim 1, including measuring devices of different measuring ranges for determining pressure loss in said boiler system for different load ranges.
 9. Flow-through steam generator according to claim 8, including automatic switch-over means between said pressure loss measuring devices for effecting load-dependent switching from one to another of said measuring devices at different load levels.
 10. Flow-through steam generator according to claim 1, including storage means for providing nominal values for comparison with the measured data, a calculating device operatively connected to said load correction regulator means downstream thereof for calculating the respective pressure loss of said boiler system for load-dependent variable operating pressure, means for continuously transmitting measurement signals representing load and steam pressure to said calculating device, and means located in the vicinity of said nominal values storage means for adjusting said nominal value. 